Know Your Friends

Eriborus terebrans, Parasite of European Corn Borer

The ichneumonid wasp, Eriborus terebrans, was introduced to the United States as part of a classical biological control project to control European corn borers. Approximately 140,000 wasps collected from both Asia and Europe were released from 1927 through 1940 in 13 states from Vermont to Virginia and as far west as Indiana and Michigan.

It became established and is currently one of the most widely distributed parasitoids of the corn borer in the north central region.

E. terebrans overwinters as a larva inside overwintering corn borers, and resumes development in the spring. Emergence of first generation wasps coincides with the first larval generation of European corn borers. Females mate soon after emergence and can lay eggs within a day after emergence.

Wasps may live 7-10 days under ideal conditions (75-80F, with access to water and sugar), but lifespan is greatly reduced (3-4 days) when temperatures are above 90F and they do not have access to sugar sources (flower nectar or aphid honeydew).

Females are highly attracted to chemicals in corn borer frass and webbing. Wasps prefer to lay eggs in 2nd-4th instar corn borers. Second generation E. terebrans adults emerge before peak numbers of second generation corn borer larvae. In Michigan, E. terebrans parasitized an average 4.9% and 18.7% of first generation corn borers, and 10.2% and 9.1% of second generation corn borers in 1989 and 1990, respectively. The highest level of parasitism by E. terebrans observed in individual fields was 37.4%, during the first generation in 1990. Previous research suggested that first generation corn borers were more likely to be parasitized by E. terebrans than second generation larvae, but this may vary from year to year. Landis and Haas reported that in most fields during the two years, E. terebrans parasitized more first generation corn borers on field edges where fields bordered wooded areas. This relationship was not seen in fields not bordering wooded areas or with second generation corn borers regardless of bordering vegetation.

Additional studies showed that female wasps die rapidly when temperatures exceed 90F. Also, wasps require a sugar source (either from a flowering plant or aphid honeydew) on a daily basis or they will die. During the first corn borer generation, prior to corn canopy closure, maximum temperatures in corn fields may often exceed 90F. Also, sources of nectar or honeydew may be scarce in the middle of corn fields. Wasps are able to survive better in wooded field borders, where there is more shade and often flowering plants or sources of aphid honeydew. First generation European corn borer larvae near wooded edges were parasitized at two to three times the rate of those in field interiors.

- Bob Wright, University of Nebraska

Based on information from:

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